Method of pickling



p 2, 1953 R. M. DREWS ETAL 2,653,115

METHOD OF PICKLING Filed Oct. 14, 1948 60 55 65 70 76' 80 P/C/rL/NG TIME SECONDS I IN V EN TORS EAL PH M- DEEWS A FOLD L%PLING & BY

A rroawsvs' Patented Sept. 22, 1953 METHOD OF PICKLING Ralph M. Drews, Cleveland, and Harold L. Farling, Garfield Heights, Ohio, assignora to Republic Steel Corporation, Cleveland, Ohio, a corporation of New Jersey Application October 14, 1948, Serial No. 54,498

Claims. (Cl. 134-9) The present invention relates generally to the art of finishing metal articles and is more particularly concerned with the novel and very economical and useful method of pickling ferrous metal articles.

It is customary in the manufacture of iron and steel articles 'to dip them into, or run them through, pickling baths of acid or alkali to loosen and remove undesired oxide scale. While satisfactory scale removal is thereby realized, this practice has several undesirable aspects. For one thing, it is not nearly as rapid as it might be and therefore must be considered as adding unduly to labor costs. Secondly, it is more expensive from the standpoint of material than it ought to be, since the solutions employed are quickly poisoned by ferrous salts and lose whatever ability they originally had to descale metal surfaces rapidly and efllciently. Attempts have accordingly been made to improve pickling methods and while these have been directed toward reducing both of these costs, no appreciable progress has 'yet been developed in either line, to the best of our knowledge. Expensive and time-consuming methods-and costly and complicated apparatus have been devised, for example, to regenerate pickle liquor for reuse in pickling processes and-to convert these liquors into useful, salable products. Efforts in these lines have, though, never been successful commercially-because of economic reasons.

According to the present invention, however, it is now possible b virtue of our surprising discovery, subsequent y to be described, to reduce very materially the time required for pickling and at the same time to increase substantially the useful life of pickling solutions. On the averag'e, pickling time can be reduced in accordance with this invention up to 50% compared to conventional widely used processes and the life of pickling-solutions can be extended'very materially.

Our discovery is that by preheating the article to be pickled to a temperature within a certain temperature range, preferably through the application of a flame directly to the article at a relatively low temperature, and then contacting the article with a pickling bath at a temperature within a certain elevated temperature range substantially below the first mentioned range, very rapid and thorough scale removal invariably results. Even more surprisingly, this result obtains if the bath employed is fouled with ferrous salts and not ordinarily suitable for commercial pickling operations carried out in the conventional way. If, as indicated above,

the preheating of the article is very rapid, as

.when a flame is applied thereto, considerable descaling will actually take place before the pickling operation. But whether the pre-heat be rapidly or slowly applied, the foregoing very desirable and advantageous results can be obtained by employing this invention.

Briefly, the method of the present invention comprises the step of contacting a ferrous metal article to be pickled and scaled with a pickling bath, the article at the time of the initial bath contact having a temperature between about- 225" F. and 400 F. and the pickling bath being maintained throughout the processing period at a temperature between about 180? F. and 210 F. For best results we prefer, however, to operate with the article and bath at temperatures of about 300 F. and about 200 F., respectively, and

in practice we have found that contact may be best effected by immersing the article in the bath in accordance with the general commercial pickling techniques.

Those skilled in the art will again a further understanding of the method of the present invention and the manner in which it is preferably carried out upon consideration of the detailed description following, reference being had to the drawings accompanying and forming'a part of this specification, in which Figure 1 is a chart showing curves plotted from data gathered in the course of experimental work upon this invention; and

Figure 2 is a schematic view of apparatus implementing the method of this invention as applied to continuous pickling of steel strip stock.

Referring to Fig. 2, it will be seen that in more detail the present method, as we prefer to carry it out, involves applying a flame to a relatively cold article to be descaled, further increasing its temperature by indirect heating means, brushing the article and removing scale loosened by the heating operations, and then contacting the article with the pickling bath while the temperature of the article is between about 225 F. and about 400 F. The article in this case is steel strip stock identified as S and it is moved continuously through the illustrated processing apparatus suitably by means including two sets of driven rolls I0 disposed on opposite sides of a preheatfumace I2 wherein strip S is heated in a flue gas atmosphere produced by burning fuel delivered through hne l3. Preliminary heating of the strip is accomplished by passing it between a pair of opposed scale burner torch assemblies I4 which apply flames to its upper and lower surfaces; but just before such heating, the strip is subjected to a water spray to insure that the strip will be as cold as possible for 3 best scale removal. Nozzles II disposed above and below strip S deliver water sprays against its upper and lower surfaces and the strip is wiped by opposed rubber rolls ll prior to contacting the heating flames. As the heated strip is moved along the line from the furnace 12, the upper and lower surfaces are consecutively engaged by revolving metal brushes II which are vacuum hooded for the withdrawal of scale dust and particles removed in the brushing operation. Supporting rolls ll maintain the strip in.

position during such brushing so that the maximum scale-freeing effect is obtained. The strip is then promptly run into a pickling bath vessel is through an opening in one end thereof and is immersed in the pickling bath 20 which is maintained at a temperature in the range indicated above. After being immersed in the bath for a predetermined time suflicient to assure the desired pickling and descaling result, the strip is removed from said bath and vessel 18, whereupon it may be water-rinsed by suitable means (not shown) to remove adhering pickling solution. It is apparent that the length of the immersion or contact time will vary from bath to bath and depending upon the type and weight of the oxide scale on the article, the kind of base metal and the type of preliminary treatment of the article, as, for instance, whether it has been flame heated and brushed, or merely brushed, or indirectlyheated and not brushed.

The composition of the bath will also have a considerable bearing upon the minimum time of pickling, a longer period being required for the same result where the ferrous salt content of the bath is greater. Consequently, inflexible limits cannot be fixed for the length of the pickling period.

Although we have indicated that we prefer to effect the necessary pre-heating treatment of the metal stock to be de-scaled by both direct and indirect means, we contemplate using either of these means alone. Thus, in accordance with our discovery described above, the novel results and advantages of our present invention will be obtained when the pre-heatingv step is carried out only by means of flame application directly to the metal stock, as well as when the stock is brought to a temperature in the critical range by indirect heating, as in furnace I2.

With regard to Fig. 1, the values represented by the several curves were determined from actual tests upon steel samples 1 inches square having a thickness of .097 inch and a total area of 4 /2 inches. The scale on these samples was broken to some extent by applying flame directly to them and the samples were freed from some of the scale by brushing them as described above. Thereupon they were immersed in one of the two pickling solutions set out below under one or the other of the two specified temperatures, all as indicated in the following tables:

4 Pickling solution consisting essentially of 15% aqueous surfuric acid (by weight). No ferrous sulfate. Balance consisting of water.

Table II solution Temperature-180,, R Solution m'lggniperaturesample Treatment Weight Treatment Wei Tjmg Loss Time 0 Nature, Seconds Percent Seconds Percent 01. t 0. 4a 40 48 61 0. 49 37 0. 51 3e 0. so 25 0. 4s 37 0. 51 29 0- 50 Pickling solution containing 14.7% sulfuric.

acid (by weight) and 19.8% ferrous sulfate, balance consisting essentially of water.

Curve A of the chart illustrates the data taken from Table I under the heading Solution Te perature=l80 F.

Curve B represents the values set forth in Table I under the heading Solution Temperature=200 F.

Curves C and D illustrate the data set forth in Table 11 under the headings Solution Temperature=180 F." and Solution Temperature=200 F., respectively.

In all these series of tests, as the chart shows, the samples were immersed in the pickling baths at four different temperatures, vis., F., 200 F., 300 F., and 400 F., thus enabling the formulation of sound conclusions as to the effects of metal temperature under various conditions of solution strength and temperature.

Having thus described the present invention so that those skilled in the art will be able to understand and practice the same, we state that what we desire to secure by Letters Patent is defined in what is claimed.

What is claimed is:

1. The method of pickling a ferrous metal article which comprises the step of contacting the article at a temperature of about 300 F. with a pickling bath at a temperature between about 180 F. and about 210 F.

2. The method of pickling a ferrous metal article which comprises the step of immersing the article at a temperature of about 300 F. in a pickling bath at a temperature of about 200 F.

3. The method of pickling a ferrous metal article which comprises the steps of applying a flame to the article and thereby increasing its temperature to between about 225 F. and about 400 F., and contacting the article with a pickling bath at a temperature between about 180 F. and about 210 F.

4. The method of pickling a ferrous metal article which comprises the steps of heating said article to a temperature between about 225 F. and about 400 F., and contacting the article with a pickling bath at a temperature between about 180 F. and about 210 F.

5. The method of pickling a ferrous metal article which comprises the steps of rapidly increasing the temperature of said article to between about 225 F. and about 400 F., removing scale from the article loosened by the heating operation, and immersing the article in a pickling bath at a temperature between about 180 F. and about 210 F.

6. The method of pickling a ferrous metal article which comprises the steps of applying a flame to the article and thereby rapidly increasing its temperature and breaking oxide scale thereon, removing broken scale from the article and immersing the article at a temperature between about 225" F. and 400 F. in a pickling bath at a temperature between about 180 F. and about 210 F.

7. The method of pickling a ferrous metal article which comprises the steps of applying a flame to the article and thereby rapidly increasing its temperature and thereby breaking oxide scale thereon, brushing the article and removing scale therefrom, and immersing the article at a temperature of about 300 F. in a pickling bath at a temperature between about 180F. and about 210 F.

8. The method of pickling a ferrous metal article which comprises thesteps of applying a flame to the article and thereby rapidly increasing its temperature, heating the article indirectly and further increasing its temperature, brushing the article and removing scale therefrom, and

immersing the article at a temperature between flame to said stock and thereby raising the temabout 225 F. and 400 F. in a pickling bath at a temperature between about 180 F. and about 210 F. 1

9, 'I'he method of pickling ferrous metal strip stock whichcomprises the steps of contacting the stock with water, then promptly applying a perature of the stock to between about 225 F. and about 400 F., and then promptly immersing the strip stock in a pickling bath at a temperature between about 180 F. and about 210 F.

10. The method of pickling a, ferrous metal article which comprises the steps of increasing the temperature of said article from about room temperature to about 300 F., and contacting the article with a pickling bath at a. temperature of about 200 F.

RALPH M. DREWS.

HAROLD L. FARLING.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,136,110 Eberhart Apr. 20, 1915 1,326,585 Feenie et a1 Dec. 30, 1919 1,334,092 Harmeling Mar. 16, 1920 1,392,780 Marsh Oct. 4, 1921 2,203,606 Whitfield et al June 4, 1940 OTHER REFERENCES Shannon: "Sheet Steel and Tin Plate" (1930). page 142. The Chemical Catalog Co. Inc., 419 Fourth Ave., New York, N. Y. 

1. THE METHOD OF PICKING A FERROUS METAL ARTICLE WHICH COMPRISES THE STEP OF CONTACTING THE ARTICLE AT A TEMPERATURE OF ABOUT 300* F. WITH A PICKING BATH AT A TEMPERATURE BETWEEN ABOUT 180* F. AND ABOUT 210* F. 